Vermont Vegetable and Berry News – February 7, 2007
Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967 ext.13,

(adapted from Cathy Heidenreich, Dept. Horticulture, Cornell University)

Pruning impacts fruit dollars in the current season, and over the life of the blueberry planting. Benefits include: Maintain bush productivity and vigor through elimination of older, less productive canes and rejuvenation of new cane growth; Facilitate harvest by developing appropriate growth habit; Increase air circulation, reducing conditions favorable for disease development; Reduce fruit number and open canopy to sunlight, improving sweetness and fruit size; Remove winter-injured, damaged, insect-infested, or diseased plant parts.

Before you prune decide on a pruning plan for your particular planting(s). What variety or planting will you do first? Does this particular variety need special pruning? Pruning stimulates vegetative growth. It follows, then, that weaker bushes will benefit from more pruning than vigorous bushes; they may also require detail pruning as opposed to complete cane removal. Special consideration is needed for varieties with spreading habits. In this case you may be tempted to remove all those canes sprawling into alley ways; care must be taken to leave sufficient canes for fruiting.

In general, prune to an upright growth habit with an open canopy allowing good light penetration. Do this in four easy steps. First, remove any damaged canes, i.e. winter injury, insect or disease damage, or breaks. Second, remove canes that rub against another cane, to prevent spread of canker diseases. Third, remove older canes and those canes obstructing movement through the alleys. Fourth, remove any short, branched canes within the canopy; fruit on these interior canes generally ripens too late to be harvested. Cut canes as close to the crown as possible. Avoid leaving stubs that become homes for canker-causing fungi. When branches are removed, make cuts as close as possible to the main cane; avoid leaving short, stubby branches for the same reason.

In 1-2 year old plantings, little pruning is required. Promote vegetative growth by rubbing off flower buds in March or April. Alternatively, prune off shoot tips where flower buds are located. In 3 year old plantings, if more than 2 new canes were produced the previous year, leave the 2 healthiest new canes; remove the remaining new canes. In 3-8 year old plantings, continue light pruning, leaving the 2-3 best new canes from previous season, until plants reach full size. Eight year old plants should have 10-20 canes of various ages. Plantings older than 8 years of age require annual removal of 8 year old canes. In general, 20% of older wood (1 out of every 6 canes) may be removed without reducing yield; berry numbers may be lower but fruit will be larger in compensation.

Do your plantings need rejuvenation? Strategy 1: Remove old, unproductive canes, leaving 2 or 3 older canes and all younger canes. In successive years, remove up to 20% of older wood until new cane growth occurs. Keep 2-3 new canes and continue to remove 20% of oldest canes. Strategy 2: Cut all canes to ground level (delays harvest 3 years), then thin new canes that arise to the most vigorous 6-10 canes. Strategy 3: Summer hedge (cut off new top growth) immediately after harvest; selectively remove dormant canes.

Pruning to reduce disease pressure in blueberries is a one-two punch. Two common blueberry canker diseases, Fusicoccum and Phomopsis, overwinter in cankered wood. These fungi are also particularly adept at colonizing dead wood, particularly pruning stubs. Removal of cankered canes and avoiding cane or branch stubs during pruning will reduce the number of new infections occurring during the season. Prune out and burn diseased canes and branches, taking care to remove all infected (brown) tissue below the cankers. Cultural practices (maintaining plant health, minimizing winter injury, and pruning out dead wood) are more important in controlling canker diseases that sprays. Canker disease severity and spread may be further minimized if new cankers are pruned out as they appear during the growing season. Pruning further reduces disease development by maintaining a growth habit with an open canopy so that all plant surfaces are exposed to good air circulation and can dry quickly.

Insect pressure may also be reduced through good pruning. Scale insect infestations are more frequently found in poorly maintained bushes; good pruning practices go a long way toward reducing scale problems. Keep an eye out for the hard-covered female insects on small twigs and branches while pruning. If scales are present, schedule a dormant oil spray for early spring during bud swell.

Insect stem galls were particularly prevalent on blueberries during the 2006 growing season. The tiny wasps overwinter as larvae in the galls. Adult wasps emerge in early June and lay eggs on twigs, causing new galls. Currently there are no products available for control of this insect. Your only recourse in this instance is to prune out and burn the galls now to reduce your insect stem galls next season. Watch during mid to late June and July for new galls. Prune out and destroy them as they appear.

Finally, brush removal is an important part of the pruning process. One method is to chop brush in place using PTO driven equipment such as Bush Hog or a flail mower. Another option may be to push brush out of alleyways and burn, chop, or chip it off site. Is the job done? Not quite. Take time next fall and winter to evaluate how well your pruning strategies for the 2007 worked, and determine what needs to be done in 2008 to keep those pruning dollars yielding better blueberries, and greater return on your investment.
Mary Jo Kelly, Marvin P. Pritts and Robin R. Bellinder, Dep. Horticulture, Cornell University

Three cultivation tools were compared with a traditional between-row cultivator, an herbicide control, and the conventional herbicide-plus-cultivator weed management program used in a first-year strawberry planting. The new implements were 1) a Rabe Werk flex-tine harrow, 2) a Buddingh finger weeder, and 3) a Bärtschi brush hoe, and the traditional implement was a double-headed multivator.

The flex-tine harrow performed poorly. Its use appeared to stimulate germination of weed seeds as end-of-season weed biomass was high and yield the following year was low. It was also the most labor-intensive treatment to maintain. The finger weeder reduced in-row weed growth dramatically, and productivity of this treatment was high, but its use required additional between-row cultivation with another implement. The brush hoe, while classified as a between-row weeder, reduced in-row weed growth as well, and yields for brushed plots were also high. Cultivation with a multivator resulted in good weed control between rows and high yields, but hand weeding requirements within the row were high.

Weed growth and yields were unacceptable when the herbicide was used alone, but an early-season pre-emergent herbicide application, followed by a single late-season hand weeding and cultivation, resulted in a dramatic reduction in weeds at the end of the year and a notable increase in yield the following year. The conventional herbicide-plus-cultivation weed management program, used in the establishment year by growers who plant in the perennial matted row system, continues to be a good choice if labor is both plentiful and affordable; however, the finger weeder and brush hoe are viable alternatives for situations in which labor is scarce. Organic growers, and growers who plant in non-traditional annual systems, may benefit from their use as well. To read the full research article, see HortTechnology January-March 2007.

(adapted from Becky Grube, University of New Hampshire)

Indar now has a national ‘section 3’ supplemental label for use on mummyberry disease in blueberries. Indar is one of the most effective fungicides for control of this disease, so conventional growers with a history of mummyberry may want to consider it. You must have the special supplemental label on hand when you use the fungicide; your pesticide dealer should provide it, or you can get it on-line at For optimum disease control (and to prevent the fungus from becoming resistant to Indar) cultural practices that reduce disease incidence should be used. These include: raking under the bushes in very early spring to disturb the apothecia before they release spores, mulching in the spring to bury the mummies and apothecia, and application of lime sulfur, urea, or concentrated fertilizer to the soil surface to ‘burn’ the apothecia. To prevent primary infections, fungicide applications should begin at bud break, or at the early green tip stage of growth. Reapply at the recommended interval (10-14 days, for Indar). Current research from Michigan State Univ. shows that Indar 75 WSP is highly effective in controlling the disease when a high amount of inoculum is present.

(for more info see click on ‘meetings’

Vermont Vegetable and Berry Grower’s Annual Meeting.
Monday, February 26, 2007, Capital Plaza Hotel, 100 State Street, Montpelier, VT

New England Greenhouse Tomato School
Wednesday, March 14, 2007. DoubleTree Hotel, Burlington, VT

Mention of pesticide or equipment names is for information purposes only. No endorsement is intended nor is discrimination against products not mentioned. Always read and follow the label.